Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Generally, a typical semiconductor device includes a substrate having active devices such as transistors and capacitors. These active devices are initially isolated from each other, and interconnect structures are subsequently formed over the active devices to create functional circuits. Such interconnect structures may include contact plugs, which may be electrically coupled to the active devices on the substrate.
A typical contact plug may include tungsten (W) due to its low resistivity (about 5.4 μΩ·cm) and high reliability. However, as dimensions of integrated circuits continue to scale to smaller sub-micron sizes in advanced node applications, it becomes an increasing challenge to reduce contact plug resistance while decreasing contact hole size. Improved structures and methods for manufacturing same are needed.